Pathology/Lab Coding Alert

Although “toenail” is an unlisted specimen, the correct surgical pathology exam code in the following case might surprise you.

See our experts’ tips for choosing the correct procedure and diagnosis codes in the following example.

Pinpoint Details as You Study the Case

Specimen(s): Surgeon separately submits a toenail and a full-thickness incisional biopsy taken under the nail for patient with pigmented “stripe” on right great toe for differential diagnosis of onychomycosis, melanonychia, or melanoma.

Pathology evaluations:

• Microscopic exam of Hematoxylin and Eosin (H&E) stained biopsy tissue
• Periodic acid-Schiff (PAS) staining of toenail shaving for fungus
• S-100 and Ki-67 immunohistochemistry (IHC) stains of biopsy tissue

Findings:

• Histopathology — abundance of melanocytes with nuclear atypia with Breslow depth < 1 mm
• PAS negative for fungal infection
• S-100 positive
• Ki-67 reported as 25 percent proliferation index

Diagnosis: Subungual melanoma in situ.

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This case requires 5 procedure codes. Here’s how to select them.

Biopsy tissue microscopic exam: Selecting the correct surgical pathology exam code means finding the specimen listed under one of the codes 88302-88309 (Level … - Surgical pathology, gross and microscopic examination …).

You should report the microscopic exam and evaluation of the biopsy tissue in this case as 88305 (Level IV - Surgical pathology, gross and microscopic examination … Skin, other than cyst/tag/debridement/plastic repair …), according to R.M. Stainton Jr., MD, president of Doctors’ Anatomic Pathology Services in Jonesboro, Arkansas.

Toenail exam: Toenail is not a listed surgical pathology specimen. A CPT^® instruction states that “any unlisted specimen should be assigned to the code which most closely reflects the physician work involved when compared to other specimens assigned to that code.” The pathology report indicates performing PAS stain on the nail, but doesn’t otherwise document a microscopic exam of the nail. That means you should assign the nail exam as 88300 (Level I - Surgical pathology, gross examination only) in this case.

Fungal stain: In addition to the 88300, you should report +88312 (Special stain including interpretation and report; Group I for microorganisms (eg, acid fast, methenamine silver)) for the toenail shaving PAS stain. Bonus tip: Instead of a PAS stain, you’ll frequently see a toenail specimen evaluated for fungus using a KOH preparation. In those cases, you would report 87220 (Tissue examination by KOH slide of samples from skin, hair, or nails for fungi or ectoparasite ova or mites [eg, scabies]). For a Medicare beneficiary, you might need to use Q0112 (All potassium hydroxide [KOH] preparations).

Immunohistochemistry: CPT^® distinguishes IHC stain codes as qualitative or quantitative/semi-quantitative. The relevant codes for qualitative IHC stains are +88341-88342 (Immunohistochemistry or immunocytochemistry, per specimen … single antibody stain procedure …). For quantitative or semi-quantitative IHC, turn to 88360-88361 (Morphometric analysis, tumor immunohistochemistry (eg, Her-2/neu, estrogen receptor/progesterone receptor), quantitative or semiquantitative, per specimen, each single antibody stain procedure …) based on whether the procedure is manual or uses an automated computer-assisted technology.

S-100 protein noted in the sample report is a characteristic IHC marker for melanoma, and pathologists typically report the findings as positive or negative for S-100, which is a qualitative result. Code the S-100 stain as 88342 (Immunohistochemistry or immunocytochemistry, per specimen; initial single antibody stain procedure).

Ki-67 is a quantitative marker for cellular proliferation that may indicate the aggressiveness of a tumor. If the pathologist manually evaluates the Ki-67 IHC stain for the biopsy specimen, report 88360 (… manual).

Roundup: Your final CPT^® code selection for this report should include 88305, 88300, 88312, 88342, and 88360.

In Situ: Get the Diagnosis Right

The pathologist reports the final diagnosis as subungual melanoma in situ.

Avoid: Although the pathologist indicates melanoma of the right big toe, you should not code the case as C43.71 (Malignant melanoma of right lower limb, including hip).

Depth: Based on the Breslow depth of < 1 mm, the pathologist designates the diagnosis as melanoma in situ. “ICD-10-CM distinguishes malignant melanoma from melanoma in situ,” says Terri Brame Joy, MBA, CPC, COC, CGSC, CPC-I, revenue cycle director for Clinical Health Network for Transformation in Houston, Texas. That’s why you should report this case as D03.71 (Melanoma in situ of right lower limb, including hip).

Differential diagnoses: Two common misdiagnoses of subungual melanoma are melanonychia, which is a dark discoloration of the nail plate, and onychomycosis, which is a nail fungal infection. The PAS stain findings ruled out an onychomycosis diagnosis. The abundance of melanocytes with nuclear atypia, S-100 positive IHC stain and the Ki-67 greater than 20 percent all indicted a diagnosis of melanoma instead of melanonychia.